Scrubbing apparatus and method

ABSTRACT

An apparatus and method for scrubbing gases with liquid. The apparatus employs a plurality of nozzles which discharge several streams of the gas downwardly against the surface of the scrubbing liquid (e.g., water). Each nozzle has a shield which overlies the liquid body and confines the movement of gas and entrained liquid from the region of impingement with the liquid. The nozzles and their shields are arranged in a cluster within a reservoir. In carrying out the method, the gas flow is discharged from the several nozzles and caused to impinge on the surface of the liquid, the flow velocity being such that depressions are formed in the liquid body immediately below the nozzles. Some initial scrubbing action is effected by such impingement, and the impingement causes some of the liquid to be entrained in the gas flow whereby a gas-liquid mixture flows outwardly in a radial direction from the region of each depression and through the spaces underlying the shields. Also, the gas-liquid mixture discharging from the region of each depression is caused to intermingle with the gas-liquid mixture discharging in an opposite direction from at least one adjacent nozzle, thereby causing further turbulence and scrubbing action. This invention relates generally to an apparatus and method for subjecting air and other gases to scrubbing with water or other liquid.

United States Patent [1 1 Mare [451 July 17,1973

[ SCRUBBING APPARATUS AND METHOD [76] Inventor: Ernest Mare, c/o JackMelvin, Kreb Engineering, 1205 Chrysler Drive, Menlo Park, Calif. 98025i [22] Filed: Jan. 28, 1972 [21] Appl. N0.: 221,638

Primary Examiner-Samih N. Zaharna Assistant Examiner-Richard W. BurksAtt0rney-Paul D. Flehr et al.

[57] ABSTRACT An apparatus and method for scrubbing gases with liquid.The apparatus employs a plurality of nozzles which discharge severalstreams of the gas downwardly against the surface of the scrubbingliquid (e.g., water). Each nozzle has a shield which overlies the liquidbody and confines the movement of gas and entrained liquid from theregion of impingement with the liquid. The nozzles and their shields arearranged in a cluster within a reservoir. In carrying out the method,the gas flow is discharged from the several nozzles and caused toimpinge on the surface of the liquid, the flow velocity being such thatdepressions are formed in the liquid body immediately below the nozzles.Some initial scrubbing action is effected by such impingement, and theimpingement causes some of the liquid to be entrained in the gas flowwhereby a gas-liquid mixture flows outwardly in a radial direction fromthe region of each depression and through the spaces underlying theshields. Also, the gas-liquid mixture discharging from the region ofeach depression is caused to intermingle with the gas-liquid mixturedischarging in an opposite direction from at least one adjacent nozzle,thereby causing further turbulence and scrubbing action. This inventionrelates generally to an apparatus and method for subjecting air andother gases to scrubbing with water or other liquid 5 Claims, 5 DrawingFigures PAIENIEDJuLmma I I 5,745,745

SHEEI a or 3 wimmgam, 7 i973 3.745.745

SHEET 3 0F 3.

H/UWWWUW FIG- SCRUBBING APPARATUS AND METHOD BACKGROUND OF THE INVENTIONIn So. African Patent 66/7061 entitled Improved Means for Carrying OutGas Scrubbing Operations, there is disclosed scrubbing apparatus makinguse of a nozzle disposed in the upper part of a reservoir that isadapted to contain a body of scrubbing liquid underlying the nozzle. Thenozzle is provided with an annular shield mounted near the lower end ofthe nozzle and spaced above the liquid surface. The gas to be scrubbedis discharged downwardly through the nozzle and caused to impinge uponthe surface of the liquid. This causes the surface of the liquid to bedepressed, and gas with entrained liquid is caused to discharge in ageneral radial direction from the region of the depression and throughthe space underlying the shield. In some instances an impingement screenis provided which depends from the periphery of the shield. Suitablemeans such as an overflow weir is provided for maintaining the level ofthe liquid body substantially constant.

The scrubbing apparatus described above is effective for performingvarious gas scrubbing operations, as for example, for the removal ofentrained dust solids from flue gases. However, when units areconstructed for the higher flow capacities the apparatus becomesrelatively expensive and considerable space is required forinstallation. Also the separating efficiency, while relatively goodcompared to many other types of conventional gas scrubbers, isrelatively inefficient compared to the efficiency obtained by thepresent invention.

In the above described prior apparatus, the scrubbing or separatingaction takes place by virtue of impingement of gas against the surfaceof the liquid body, and particularly against the surface of thedepression formed in the body. Also scrubbing takes place by virtue ofintermixture of gas with entrained liquid in the confined space belowthe shield. The present invention is predicated upon the discovery thatimproved scrubbing action can be obtained when the gas flow is dividedinto a plurality of streams which are directed downwardly against thesurface of the liquid body, and particularly when the apparatus isconstructed to provide a cluster of nozzles, each with its individualshield. As will be present explained, one of the principles involved isthat the combined perimeter of a plurality of discharging nozzles of agiven cross-sectional flow area is substantially greater than theperimeter of a single nozzle of the same cross-sectional flow area, andextended perimeter length by use of a plurality of nozzles promotesscrubbing efficiency.

Further, the combined surface area of depressions made by the samevolume of gas passing through a cluster of nozzles as above described isconsiderably larger than the surface area of the single depressioncaused by the same gas flow through one nozzle of equivalent dischargearea.

SUMMARY OF THE INVENTION AND OBJECTS In general, it is an object of thepresent invention to provide novel gas scrubbing apparatus which issuperior in many respects to the apparatus and method disclosed in saidSouth African patent.

Another object of the invention is to provide a gas scrubbing apparatuswhich for a given capacity is relatively compact and economical tomanufacture.

Another object of the invention is to provide a gas scrubbing apparatusand method which is characterized by superior separating action.

Another object of the invention is to provide apparatus of the abovecharacter which requires relatively low power consumption for a givencapacity.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments have been setforth in detail in conjunction with the accompanying drawing.

BRIEF DESCRPTION OF THE DRAWING FIG. 1 is a side elevational view insection schematically illustrating apparatus incorporating the presentinvention.

FIG. 2 is a cross-sectional view in section taken along the line 2 2 ofFIG. 1.

FIG. 3 is a detail showing the addition of impact screens.

FIG. 4 is an end view in section schematically illustrating apparatus ofgreater capacity, having a large number of discharging nozzles.

FIG. 5 is a side elevational view of the apparatus shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus illustrated inFIG. 1 consists of a reservoir 10 which is shown provided with a conicalshaped lower portion 11 to facilitate the settlement and removal ofsolids. The lower end of the reservoir is shown connected to a drainpipe 13 which may be provided with the valve 12. In operation a body ofliquid 14 is maintained in the reservoir.

Suitable means is provided, for maintaining the level of the liquid bodysubstantially constant. For example, liquid may be bled into the bodythrough a float valve which automatically supplies additional fluid whenthe level falls. As another expedient for this purpose, the reservoircan be provided with an overflow box 16 connected to the drain pipe 17,together with an adjustable weir 18 which controls flow of liquid intothe box.

The gas flow to be subjected to scrubbing is introduced into themanifold 21 which in turn communicates with the downwardly directednozzles 22 within the upper part of the reservoir. It is desirable butnot essential that these nozzles be conical shaped as illustrated. Thelower open end of each nozzle is spaced a short distance above thesurface of the liquid body 14. An annular shield 24 is mounted upon thelower end of each nozzle, preferably a short distance above the lowerend 23. These shields are dished with their concave sides faced upwardlyand each shield serves to provide an upper confining wall for the spaceunderly ing the same.

The upper part of the reservoir 10 connects with a gas discharge conduit26. A suitable liquid eliminator 27 can be provided for removingentrained liquid from the gas flow, and liquid so removed may be drainedback to the reservoir 10 through pipe 28.

It is desirable to arrange the nozzles 22 in the form of a cluster. FIG.2 illustrates a cluster consisting of four such nozzles disposed withtheir axes parallel and vertical and with the shields 24 spaced apart asindicated at 29. This spacing is preferably substantially less than theradius of each shield 24, for example one-half to one-fourth of suchradius. It should be understood that in some instances only two nozzlescan be used, and in other instances, three, four, or many more nozzlescan be arranged as a cluster. In general, three or more nozzles arepreferred.

Operation of the apparatus and the present method can be explained byreference to FIGS. 1 and 2. Assuming that a gas flow, for example stackor flue gas contains dust particles that are to be removed, the flow isdirected into the manifold 21 and divided into a plurality of streamswhich discharge downwardly from the lower ends 23 of the nozzles 22. Itis desirable for the gas flow velocity from the lower end of each nozzlebe of the order of 10,000 ft. per minute or higher. The discharging gasstreams impinge upon the surface of the liquid body 14, with the resultthat a pronounced liquid depression is formed immediately below eachnozzle. Such impingement exerts a scrubbing action on the gas, withseparation and entrapment of dust particles in the liquid. In addition,the gas flowing upwardly and out from each depression 31 picks up andentrains liquid, whereby the gas discharging outwardly through thespaces 31 below the shields 24 is in fact gas with entrained fluid, orin other words, a gas-liquid mixture. The liquid existing in this flowmay be in part relatively thin liquid films and in part droplets ofvarying size. Some turbulence also occurs in the annular spaces 32, withthe result that there is effective contact of gas with surfaces ofentrained liquid, thus promoting wetting of solid particles withentrainment of solid particles with the liquid. The flow occurringoutwardly from the lower end of each nozzle is in effect a radiallydirected flow with a substantial amount of turbulence. However, theradial velocity decreases due to the expanding flow area. In addition,the velocity decreases radially due to expansion in a vertical directionbecause of the dished nature of the shields 24.

In FIGS. 1 and 2 the entrained liquid discharging outwardly from thelower end of each nozzle is indicated by short arrows, while the gasflow is indicated by longer arrows. It will be seen that the entrainedliquid permeates a space underlying each shield 24 extending for asubstantial distance beyond the perimeter of each shield. Gas relativelyfree of entrained liquid flows upwardly for discharge through conduit26. The gasliquid mixture discharging radially from each depressionextends beyond the periphery of each shield 24. Thus such discharge fromflowing radially from one nozzle intermingles with a like dischargeflowing in an opposite direction from an adjacent nozzle, in the regionsof the regions 34. Since both gas and entrained particles move into suchcommon regions at relatively high velocities, and in oppositedirections, the comingling of the flows creates added turbulence whichagain promotes efficient and effective scrubbing action.

Previous reference has been made to a new principle utilized in thepresent invention. The scrubbing action occurring by virtue ofimpingementof gas upon the surfaces of the depressions 31 is dependentin part upon gas impinging upon the steep side surfaces 310 of thedepressions. Also it is dependent in part upon the pe rimeter of theorifice through which the gas is discharg ing. It can be demonstratedmathematically that when, say, four nozzles are used to provide adesired total cross-sectional flow area, the sum of the perimeters ofthe four orifices is greater than a single discharge orifice of the samecrosssectional flow.

It can also be shown that the surface area of the depressions made bythe gas flow through the four nozzles is greater than that of the singledepression caused when a single nozzle of equivalent discharge area isused.

According to my observations, the additional perimeter length andsurface area of the depressions gained by the use of a plurality ofnozzles results in more efficient and effective scrubbing actioncompared to the use of a single orifice, even though the dischargingvelocity for impingement against the liquid is the same. The longerperimeter and surface area of the depressions provided by multiplenozzles serves to deliver a greater percentage of the discharging gasagainst the side inclined surface 31a where the scrubbing action ishighly effective due to the arcute angle between the direction of thegas flow and the side surface 31a.

Because of more efficient scrubbing action obtained by use of aplurality of nozzles, it is possible to construct apparatus for a givencapacity which is relatively compact and inexpensive compared to using aplurality of units of the type disclosed in said South African patent.In addition, the scrubbing action is improved. It has also been foundthat with the present invention using a plurality of nozzles, thepressure drop across the apparatus for a given capacity is relativelylow. Thus for equipment operating at a given capacity, the powerconsumption is substantially less than when utilizing apparatus of thesame capacity but of the type shown in said South African patent.

With respect to saving in cost of manufacture for a given capacity, itmay be noted that shields 24 can be mounted directly upon the nozzles 22without the use of a supplemental mounting structure. This is becausethe shields need not be of large diameter.

In some instances it may be desirable to make use of a screensurrounding the lower end of each of the nozzles and depending from theperimeter of the shield 24. As shown in FIG. 3, such a screen 36 isshown attached to the perimeter of the shield 24 and is of sufficientlength that its lower portion is immersed in the body of liquid. Thisscreen can be made of wire mesh or from circumferentially spacedvertical rods. It functions as an impact surface against which entrainedliquid impacts, thus causing entrained liquid to be broken up intosmaller droplets.

The larger capacity apparatus shown in FIGS. 4 and 5 makes use of areservoir 37 which is relatively long compared to its width, and whichunderlies the mani fold or plenum chamber 38. Inclined lower walls 39and 40 provide settling troughs which connect with the drain pipes 41.One or more overflow boxes 43 can be provided together with an overflowweir 44. The plenum chamber 38 connects with the downwardly extendingconduits 46 which in turn communicate with the conical shaped nozzles47. Each of these nozzles carries an annular shield 48 corresponding tothe shields 24 of FIG. I. The nozzles are shown arranged in twoside-by-side rows distributed along the length of the reservoir. Gas isremoved from the upper part of the reservoir 37 through one or moreconduits 51, each of which may be provided with an eliminator 52. Eachof the nozzles 47 may be provided at its upper end with one or moreducts 53 for the tangential introduction of a steam of liquid.Introduction of liquid at this point, which may be the same liquid asthat in the reservoir, tends to prevent accumulation of solids in theinner surface of the nozzles and also aids the scrubbing action.

In general, the embodiment illustrated in FIGS. 4 and 5 operates in thesame manner as the first described embodiment and the principlesinvolved are the same.

In the foregoing, particular reference has been made to the use of theinvention in the separation of dust particles from gases. However, theinvention is also applicable where it is desired to remove gaseouspolutants from industrial waste gases by scrubbing action with water orother liquid. in some instances, both solid dust particles may beremoved, together with absorption of gases. Also the invention can beused where it is desired to effect aeration of a liquid medium as forexample, the introduction of atmospheric air or oxygen into water. inaddition, the apparatus may be used to promote chemical reactionsbetween liquid and gases. All of the foregoing is embraced in what iscommonly known as a scrubbing action.

I claim:

1. A method of effecting scrubbing of gas flow with a liquid, the methodmaking use of a liquid body to gether with means for directing anddischarging gas to be scrubbed against the surface of the liquid bodyand shielding means overlying the surface of the liquid, the methodcomprising separating the gas flow into a plurality of gas streams,directing the plurality of gas streams downwardly toward the surface ofthe liquid body to cause the streams to impinge upon the liquid surface,the flow velocity against the liquid being such as to cause the liquidsurface to be depressed in the regions of impingement with entrainmentof liquid from the body and with free flight of such entrained liquidfrom each depressed region, and confining the vertical dimension ofspaces surrounding such depressed regions by said shield means wherebyflow of gas with en trained liquid occurs in a direction generallytransverse to each of said gas streams between the surface of liquid andthe corresponding shield means.

2. A method as in claim 1 in which the mixture of gas and liquiddischarging from each of said streams is caused to commingle withturbulence with the gas and entrained liquid discharging from at leastone adjacent stream.

3. In gas scrubbing apparatus, a reservoir adapted to contain a body ofscrubbing liquid, a plurality of gas nozzles disposed within thereservoir above the surface of the liquid body, said nozzles beingdisposed to discharge gas downwardly upon the surface of the liquid bodyin spaced regions, manifold means for delivering flow of gas to bescrubbed into said nozzles, and a generally horizontal shield mountedupon each of the nozzles adjacent the lower discharge end of the same,discharge of gas from said nozzles being caused to impinge upon thesurface of the liquid and to depress the liquid surface in regionsimmediately underlying the nozzles, each of said shield means serving toprovide a confined annular space between the same and the surface of theliquid, whereby gas after impingement with the liquid body flowsoutwardly with entrained liquid in directions through the confinedannular space transverse to the gas discharge to promote scrubbingaction between gas and liquid.

4. Apparatus as in claim 3 in which the shield for each of said nozzlesis circular in plan, the shields of adjacent nozzles being spaced apartby a distance which is substantially less than the radius of eachshield.

5. Apparatus as in claim 4 in which said nozzles and associated shieldsare arranged as a cluster within the reservoir.

2. A method as in claim 1 in which the mixture of gas and liquiddischarging from each of said streams is caused to commingle withturbulence with the gas and entrained liquid discharging from at leastone adjacent stream.
 3. In gas scrubbing apparatus, a reservoir adaptedto contain a body of scrubbing liquid, a plurality of gas nozzlesdisposed within the reservoir above the surface of the liquid body, saidnozzles being disposed to discharge gas downwardly upon the surface ofthe liquid body in spaced regions, manifold means for delivering flow ofgas to be scrubbed into said nozzles, and a generally horizontal shieldmounted upon each of the nozzles adjacent the lower discharge end of thesame, discharge of gas from said nozzles being caused to impinge uponthe surface of the liquid and to depress the liquid surface in regionsimmediately underlying the nozzles, each of said shield means serving toprovide a confined annular space between the same and the surface of theliquid, whereby gas after impingement with the liquid body flowsoutwardly with entrained liquid in directions through the confinedannular space transverse to the gas discharge to promote scrubbingaction between gas and liquid.
 4. Apparatus as in claim 3 in which theshield for each of said nozzles is circular in plan, the shields ofadjacent nozzles being spaced apart by a distance which is substantiallyless than the radius of each shield.
 5. Apparatus as in claim 4 in whichsaid nozzles and associated shields are arranged as a cluster within thereservoir.